i've got a few questions/comments about this.
this would really only work with your standard sliced loaf, pref. a large white warburtons style or mighty white (does that still exist)
wholemeal i think would be a disaster as it'd go to bits quicker than a leper in a wind tunnel.
round my way, your average bocadillo would be no good for window cleaning. the hard part of the baguette wouldn't absorp or clean anything. i guess you could cut it in half and use the inside half, but then it's not a sandwich. if it's a sandwich, you couldn't use the inside half, cos it'd have butter or some filling on it. you'd literally be putting dirt on the window as you were cleaning it.
i guess you could use a variant like soda bread or something, something designed to soak **** up. i dunno 5 x the water of your average sliced bread......like those kitchen roll adverts.
also you couldn't toast the sandwich cos the grease off it would cause all sorts of hassle on the clean up operation. some might say toasting it automatically means it's not a sandiwch, it's actually a toastie. but some call it a toasted sandwich. that's a whole other debate though, so let's just deal with the sandwich window cleaning thing first.